Motor vehicles that are driven by an electric machine are being developed and/or manufactured by the automotive industry in ever-increasing numbers. The electrical power for operating the electric machine for driving the electric vehicle originates from a battery situated in the electric vehicle. The battery is charged at a power supply when the electric vehicle is at a standstill. The electric vehicle includes a charger unit for this purpose. The capacity for storing electrical power in the battery is limited, so that the electric vehicle is able to achieve ranges of only approximately 50 km to 200 km. To increase the range of the electric vehicle, it is provided with a so-called range extender (an internal combustion engine-generator unit). For fairly long trips of the electric vehicle, during which the battery is not chargeable or is not sufficiently chargeable by a power supply, the internal combustion engine-generator unit charges the battery, and/or the internal combustion engine-generator unit supplies electrical current to the electric machine. The possible range of this type of electric vehicle having a range extender may thus be extended to ranges which correspond to those of conventional motor vehicles driven solely by an internal combustion engine.
The electric machine of the motor vehicle is operated both as an electric motor and as a generator. During operation as an electric motor, the electric machine is used to drive the motor vehicle, and during operation of the electric machine as a generator in regenerative mode, the electric machine is used to decelerate the motor vehicle or hybrid vehicle. If operation of the internal combustion engine-generator unit is necessary while driving the hybrid vehicle, the electrical power provided by the internal combustion engine-generator unit is used to operate the electric machine as an electric motor and also to charge the battery. A deceleration or a braking operation of the hybrid vehicle may occur during this type of operation. During a deceleration operation of the hybrid vehicle, the electric machine is switched from operating as an electric motor to operating as a generator, and thus generates electrical power for charging the battery. However, the internal combustion engine-generator unit is also still operating, so that the electrical charging capacity of the battery is composed of the electrical power of the electric machine as a generator and also of the electrical power provided by the internal combustion engine-generator unit. This may result in overvoltages in the charging voltage of the battery, or a high charging current, which may result in damage to the high-voltage components of the hybrid vehicle, in particular the battery.
German Patent Application No. DE 10 2008 039 907 describes a vehicle having a power source, an electrical power store, a generator which is designed to generate electrical power and to charge the electrical power store, an electric traction motor, and an activating device which is designed for switching the power source on and/or off, a starter device having a control element which initiates the switch-on and/or the switch-off of the power source by the activating device, the control element being designed in such a way that it allows the initiation without the driver having to be in the vehicle at the time of the initiation.